Magnetometry involves taking surveys of a portion of the surface of the Earth (or another body). Magnetic surveys are commonly conducted from airborne, sea surface, undersea and/or ground-based platforms. Such surveys are typically performed commercially for the oil, gas and mineral exploration industries by surveying companies that specialize in magnetometry. Airborne surveys are generally performed from either fixed wing aircraft or helicopters using scalar magnetometers (See, e.g., FIG. 1A (commercial magnetic survey aircraft 100 with three total field scalar magnetic sensors 102, 104 and 106), and 1B (military aircraft 108 with single total field scalar magnetic sensor 110)). Undersea surveys are generally performed by towing a sensor suite behind a boat or ship (See, e.g., FIG. 1C (sensor sled 112 with single total field scalar magnetic sensor 114 shown out of the water), and 1D (sensor sled 112 being towed through the water with the magnetic sensor submerged by at least some amount)). Ground-based surveys may be performed by towing a magnetically quiet cart behind a land vehicle (See, e.g., FIG. 1E (sensor cart 116 configured to be towed by a land vehicle)), with a push cart, or with a handheld or body-mounted sensor system (See, e.g., FIG. 1F (human-mounted magnetic sensor suite 118). Magnetic surveys are also performed in military applications to locate buried or submerged objects of interest such as buried explosive devices. The goal of such surveys is to find and locate magnetic anomalies which may be of interest. If the object of interest has moving metal parts, it may also emit alternating magnetic fields known as extremely low frequency emissions (ELFE) which magnetometers can also detect. In the mining and oil and gas industry it is known that certain types of rock formations with particular magnetic signatures can be a clue to nearby materials of interest. In archeology and environmental site remediation, buried iron and steel objects can be found. In the military certain magnetic signatures may indicate the presence of hostile underwater craft and buried unexploded ordnance, or explosive devices. Performing a magnetic survey typically involves moving the sensor suite over the various locations in a grid of interest. FIG. 1G illustrates a typical area of interest 120. The area is divided by horizontal and lateral raster scan lines 122, 124 over which the sensor suite will be carried by the platform to accomplish the survey. Depending upon the goals of the survey and the equipment being used, the distance between adjacent horizontal and lateral lines may be adjusted for best results as desired.
In the past such surveys have either been conducted in real time without significant efforts at real time noise reduction or they have been conducted with the benefit of offline noise reduction at the cost of several hours or days of additional time delay between the time of the survey and the receipt of the survey results. In military applications this delay will usually be considered undesirable and in commercial applications, while acceptable in certain circumstances, this approach gives one no opportunity for a mid-course correction, i.e., if the location appears wrong, or the equipment is not operating properly, the opportunity to go to another location or where useful data appears is or the opportunity to adjust or repair the equipment without carrying out a useless survey is not possible due to the delayed review of the survey results. This adds significant costs both in time and money.
A real time (e.g., survey results available reasonably quickly (seconds or minutes as opposed to hours) after measurements take place) noise reduction capability would be of great value to all parties interested in magnetometry.